AER2: Lift Flashcards
Define Camber
The maximum distance between the chordline and the mean camber line
Define Chordline
A straight line running from the leading edge to the trailing edge of the wing.
Define Mean Camber line
Line marking the middle of the wing, taking into account the curve of the aerofoil.
Define relative airflow
The relative direction and speed of the air before it is influenced by the presence of an aircraft. Always equal and opposite to the flight path.
Define Angle of Attack
The angle between the chordline of the wing and the relative airflow.
Define Air density
Is the mass of the air per unit of volume (Mass/Volume). Is given the greek letter (p) or rho.
Define the aerofoil section
The wing of the aircraft, produces more lift than drag with a streamline rounded leading edge and sharp trailing edge.
Define Static pressure
Pressure due to molecular motion at rest and atmospheric pressure.
Define Dynamic pressure
Pressure caused due to motion
Define total air pressure
Static plus dynamic is total air pressure.
Define Bernoulli’s theorem and explain how this relates to a wing.
In a duct, when airflow is accelerated, static pressure drops. This is seen on a wing, when the relative airflow over the top of the wing is accelerated, producing Low pressure over the top of the wing. The airflow underneath the wing is not accelerated, producing a High pressure system underneath. This produces lift.
Define Co - efficient of lift
The aircraft’s ability to produce lift. (via the aerofoil).
What is the Co - efficient of lift affected by?
- Aerofoil shape (constant)
- Angle of attack (not constant) as this increases, so too does the value of cL.
Aerofoil surface area (constant)
(think about the equation!)
What is the name of the maximum angle of attack?
The critical angle. Exceed this and you will stall the aircraft.
What happens generally when you increase the angle of attack?
There will be an increase in the curvature of the aerofoil, an increase therefore in the airflow acceleration over the top of the wing, and an increase in the pressure on the top of the wing. Lift will as a result increase also.
What is the equation for lift?
L = cL x p x v2 x S
2
Where: L = Lift p = rho (air density) cL = co - efficient of lift v = Airspeed s = Surface area of the wing.
Define centre of pressure
Is the point on the chordline through which the total aerodynamic reaction is considered to act. (lift and drag)
Define total reaction
The resultant of all aerodynamic forces acting on the wing of the aircraft.
Identify some lift/drag devices of an aircraft
Flaps, slats, slots, spoilers, speed brakes.
Define Flaps
Alter the camber of the wing and can lengthen the chordline to produce more lift.
Define Slats/Slots
Aerofoils attached to the leading edge of the wing, provides an energised air channel that activates the upper layer of the wing, increases lift at high angles of attack. Slots provide a corridor for air to pass through under the slat.
Define Spoilers and speed brakes
Spoilers are located on wings and ‘spoil’ the airflow over the upper surface, increasing drag and reducing lift. Speed brakes are located in many places (think F-15). Increase drag.
Define stalling
Stalling occurs when there is a breakdown of streamlined airflow over the upper surface of the wing. The turbulent air no longer produces the decreased pressure on the top of the wing and lift is decreased as a result. This is the critical angle/Stall angle.
Recovery from Stalling
Attitude down, increase speed.
Define centre of pressure
The point, usually on the chordline, through which the total reaction is considered to act.
Define centre of gravity of the aircraft
The point of balance where the total weight of the aircraft acts through.
